Benzathine as a cause for a false-positive test result for amphetamines

LC-MS-MS vs ELISA: Validation of a Comprehensive Urine Toxicology Screen by LC-MS-MS and a Comparison of 100 Forensic Specimens

Toxicology laboratories commonly employ immunoassay methodologies to perform an initial drug screen on urine specimens to direct confirmatory testing. Due to limitations of immunoassay testing and the need to screen for a broader range of drugs with lower limits of detection at a lower cost, mass spectrometry screening techniques have gained favor in the toxicology field. A liquid chromatography-tandem mass spectrometry (LC-MS-MS) urine screening panel was developed and validated for 52 drugs and metabolites. A simple dilute-and-shoot with enzymatic hydrolysis technique was utilized to prepare the urine specimens for analysis. Limit of detection, interference, ionization suppression/enhancement, carryover and stability of processed specimens were assessed during validation. To evaluate the toxicological results obtained from utilizing the LC-MS-MS in comparison with the laboratory's current enzyme-linked immunosorbent assay (ELISA) panel, 100 authentic urine specimens from suspected driving under the influence and drug-facilitated crime cases were analyzed using both methodologies and the results were compared. In addition, the cost of each methodology was evaluated and compared. The validated LC-MS-MS method had limits of detection that were equal to or lower than the concentrations validated for ELISA cutoffs, had fewer exogenous interferences, and the cost of screening per specimen was reduced by ~70% when compared to ELISA. Comparing the toxicology results of forensic urine specimens demonstrated that by only using ELISA, the laboratory was unable to detect benzoylecgonine in 26%, lorazepam in 33% and oxymorphone in 60% of the positive specimens. Additional analytes detected using the LC-MS-MS method were zolpidem and/or metabolite, gabapentin, tramadol and metabolite, methadone and metabolite, meprobamate and phentermine. The results of the validation, the toxicological result comparison and the cost comparison showed that the LC-MS-MS screening method is a simple, sensitive and cost-effective alternative to ELISA screening methods for urine specimens.

Interferences With Urine Drug Screens

Qualitative urine drug assays are frequently used in conjunction with opioid contracts as a means of monitoring use of prescribed controlled substances as well as concurrent use of illicit substances in patients receiving opioids for chronic nonmalignant pain (CNMP) management. Appropriate use of these screening tests, in conjunction with opioid contracts, may provide the health care provider with additional information needed to safely prescribe opioids for selected individuals with CNMP. It is important for the practitioner caring for patients subject to random urine drug screening to understand interferences with the commonly used urine drug assays, as well as knowing options to confirm contested test results. We reviewed the literature on urine drug assay test interferences and present a summary of this information in this article.